1. Field of the Invention
The present invention relates to an audio reproduction system.
2. Description of the Related Art
A video audio reproduction system called a home theater system is spreading. In the video audio reproduction system, for example, video reproduction from a DVD (Digital Versatile Disc) is performed by displaying a video on a relatively large-screen display and a multi-channel surround audio system is adopted and, recently, a 5.1-channel system is adopted for audio reproduction. This makes it possible to realize powerful video and audio reproduction.
In the audio reproduction system of the 5.1-channel system, four kinds of speakers are necessary: a speaker in front of a listener (hereinafter referred to as “front”), a speaker right in front of the listener (hereinafter referred to as “center”), a speaker behind the listener (hereinafter referred to as “rear”), and a speaker exclusively used for low frequencies. A subwoofer, which is a speaker exclusively used for low frequencies, monaurally covers bands equal to or lower than 100 Hz. The other speakers cover bands from 100 Hz to 20 kHz.
In the past, as a speaker arrangement in the audio reproduction system of the 5.1-channel system, a speaker for a front left channel, a speaker for a front right channel, and a speaker for a center channel are arranged on the left side, the right side, and the front of the listener, respectively. A speaker for a rear left channel and a speaker for a rear right channel are arranged on the left side and the right side behind the listener, respectively. A subwoofer speaker for an LFE (Low Frequency Effect) channel (exclusively used for low frequencies) is arranged in an appropriate position.
These six speakers are attached to speaker boxes and arranged in the respective positions, respectively. Usually, a distance between the six speakers in the front and rear and the listener is set to, for example, about 2 meters.
In the audio reproduction system in the past, for example, speaker boxes with a capacity of about 15 liters used for speakers for front left and right channels are changed to small boxes with a capacity of about 1 liter. The speakers are also called satellite speakers. Naturally, the speakers do not cover low frequencies. Therefore, one speaker exclusively used for low frequencies called a subwoofer is added to supplement the speakers. When the speakers other than the subwoofer are speakers of small boxes in this way, a crossover frequency of an audio signal supplied to the subwoofer is often as high as 150 Hz, which is slightly higher than 100 Hz described above. However, this is still a fairly low frequency.
In a speaker system including the speakers arranged as described above, when a 5.1-channel audio signal from a DVD is reproduced, naturally, bass is reproduced sufficiently. Moreover, since the channel is specially provided on the reproduction side exclusively used for low frequencies, unprecedented heavy bass echoes around a room from a source such as a movie. As a result, powerful realistic sensations can be obtained.
However, in a relatively small room in a house, it is difficult to secure a space for arranging the six speakers for reproducing multi-channel surround sound and noise due to sound leakage to the outside occurs.
In the usual 5.1-channel speaker configuration, in order to reproduce powerful sound in DVD video audio entertainment, sound volume equal to or higher than 90 dB is necessary. Therefore, when a listener attempts to satisfactorily obtain a multi-channel surround effect, the listener needs to take into account the noise to the outside.
In this case, in general, since high-frequency sound is easily insulated, it is possible to considerably attenuate the sound with a wall or one door. However, in the case of low-frequency sound such as sound at a frequency equal to or lower than 100 Hz, sound insulation is not easy. In the relatively small room of the house, a size of the room enough for insulating the low-frequency sound is often not secured. In particular, bass such as that at frequencies 50 Hz and 40 Hz covered by the subwoofer echoes and is propagated to a considerably large range.
Therefore, when sound is reproduced from the subwoofer, it is likely that the sound reaches not only the next room but also rooms above and below and disturbs residents in the rooms. In particular, it is more difficult to insulate sound at lower frequencies. The user of the subwoofer is a significant problem in the housing situation in the metropolitan region. Therefore, the valuable 5.1-channel audio reproduction system may not be able to be fully utilized under the present situation.
When the audio reproduction system is set in an automobile, the sound at low frequencies often poses a problem.
In order to solve the problem, JP-A-5-95591 proposes a sound reproduction system that reproduces medium and high registers with a small speaker (a speaker unit of which is housed in a speaker box) and reproduces low register near the ears of a listener with headphones for low register or bone conduction.
According to the technique disclosed in JP-A-5-95591, since low register is reproduced near the ears of the listener by the headphones or the bone conduction, even if the listener hears the sound at large volume, it is possible to prevent the sound from being transmitted to the house next door.